1. Field of the Invention
The present invention relates to an optical communication system and method in which a plurality of optical communication apparatuses are connected to each other in a star-like shape.
2. Related Background Art
Optical fiber communication has been used in various fields such as a computer network and an audio interface in recent years.
To perform communication between remote communication apparatuses, it is insufficient to only transmit/receive data to be transmitted, and it is necessary to simultaneously transmit clock information or share the same clock information. For example, a conventional computer network such as FDDI uses a self synchronizing method in which data containing clock information therein is transmitted in one transmission system. In the self synchronizing method, as shown in FIG. 1, a clock extraction circuit 1802 extracts a clock from a signal photoelectrically converted by an O/E converter 1801. The clock need to be reproduced by a PPL (Phase-Locked Loop) circuit 1803 on a receive side.
In the above prior art, however, follow-up properties must be intentionally degraded to remove a jitter from the receive clock by the PPL circuit and stabilize the clock. This leads to an increase in overhead for channel connection, resulting in a low transmission speed. For this reason, this method cannot be applied to a channel requiring frequent connection switching. A digital PPL is used as a PLL technique for allowing high-speed locking. In this method, a counter is used as a VCO (Voltage-Controlled Oscillator), and a frequency much higher (preferably about 32 times) than a reproduction clock is necessary for original clocks. For this reason, this method cannot be applied to optical transmission using a clock frequency of about 100 MHz.